1. Field of the Art
This invention relates to a method and an apparatus for drying substrate plates, for example, thin substrate plates of a rectangular shape as used for LCD (liquid-crystal display) panels or thin substrate plates of a circular shape.
2. Prior Art
For instance, a TFT (thin film transistor) type LCD panel generally employs a couple of glass plates as substrates, i.e., a TFT substrate and a color filter substrate. In the fabrication process of TFT substrates, TFT elements are formed on the surface of a glass plate by successively processing same through a number of steps such as formation of a thin film layer, formation of a resist film layer, exposure to light, development, etching and defoliation of the resist film. While being processed through these steps, each TFT substrate needs to be washed and dried repeatedly before or after each step. Similarly, color filters are formed on thin glass plates by a photolithography process or the like, in which each color filter substrate needs to be washed and dried repeatedly as a pretreatment before respective steps of the fabrication process. Aside from the TFT type, LCD panels or other rectangular substrate plates of glass or of synthetic resin are often required to be washed and dried before proceeding to a predetermined treatment of a fabrication process.
For drying washed substrate plates of this sort, there have been known various methods in the art. In order to continuously wash and dry substrates which are transferred on a processing line, namely, in the case of the so-called in-line processing, it has been the general practice to employ a drying method utilizing air knife effects, for example, an air knife drying method as described below.
Normally, substrate plates are transferred by a roller or belt conveyer, with faces of the respective substrate plates in a horizontal position or in a slightly tilted state in a lateral direction or in a direction perpendicular to the substrate transfer direction, and an air blasting zone is at a predetermined position in a substrate transfer path. Located in the air blasting zone is an air knife which is so disposed as to confront face to face successively with substrate plates being transferred. The air knife is provided with a nozzle mouth in the form of a narrow slit-like opening to spurt out jet air under high pressure in the fashion of a knife blade across the width of the substrate plates thereby to scrape droplets or liquid films off the surfaces of the substrate plates.
In this regard, jet ai is spurted out from the air knife nozzle from a direction opposite to the substrate transfer direction and at an angle smaller than 90 degrees, preferably, at a shallow angle of 45 degrees or smaller than 45 degrees. Besides, the nozzle mouth is located in the vicinity of substrate surfaces, so that jet air which is spurted out in the shape of a thin knife blade is impinged on substrate surfaces. As a result, liquids which have deposited on the substrate surfaces are pushed rearward in the substrate transfer direction under the pressure of the jet air and finally purged from rear edge portions of the substrate.
In this connection, in order to remove liquids and moisture from substrate surfaces in transfer more smoothly and in a more reliable manner, it is desirable to locate an air knife nozzle in a plane which is parallel with the substrate transfer surface of the conveyer, and at the same time to locate the air knife nozzle in an angularly inclined position relative to a direction perpendicularly intersecting the substrate transfer direction to spurt jet air toward substrate surfaces from a slant direction. When so located, liquid films and droplets on a substrate surface are pushed by the pressure of jet air not in a direction parallel with the substrate transfer direction but in an askew direction which corresponds to the inclination angle of the air knife nozzle. Therefore, liquids are urged to leave a substrate from rear end edge portion and from posterior side edge portions, smoothly and quickly after flowing over shortened distances along the surface of the substrate.
In order to more efficiently peel off liquid films from the surface of a substrate by the use of an air knife, it is desirable to blast jet air on substrate surfaces with as shallow an angle of incidence as possible. This is important especially at the time when a leading end of a substrate plate enters an air blasting zone of an air knife, because blasting of jet air at a deep angle of incidence will result in increased possibilities of liquid being scattered around under the pressure of jet air. Therefore, it is desirable for jet air to be impinged on substrate surfaces with as shallow an angle of incidence as possible. In this regard, the term xe2x80x9ca shallow angle of incidencexe2x80x9d means an angle which is nearly parallel with a substrate surface, while the term xe2x80x9ca deep angle of incidencexe2x80x9d means an angle which is nearly normal to a substrate surface.
In the drying stage using an air knife nozzle, liquids on the surface of a substrate plate are caused to gather in a rear corner portion of the substrate plate at a point immediately before a final liquid purging position where the substrate plate leaves the air blasting zone of the air knife. However, in that corner portion, the substrate plate no longer has a surface for guiding the gathered liquids. Therefore, especially in a case where a liquid deposits on substrate surfaces in a relatively large quantity, it may become difficult to apply the pressure of jet air effectively for completely purging the gathered liquid from corner portions of the substrate plates. If the substrate plates with liquid residues in corner portions are sent forward to a next stage of the fabrication process, the residual liquid can be caused to flow back onto the substrate surfaces by vibrations to which the substrate plates are subjected in the course of the transfer to a next processing state, contaminating the once-dried substrate surfaces again by developing stains or the like thereon. The liquid can be purged to a satisfactory degree in a case of substrate plates of small sizes on which the liquid concentration in corner portions is relatively small. Alternatively, the liquid can be purged completely from corner portions of the substrates if the substrate transfer speed is slowed down sufficiently for this purpose.
In the fabrication process of LCD panels, however, from the standpoint of production efficiency, it is the general practice to produce a mother or matrix of a large size, which is later cut into a unit size corresponding to the size of individual LCD panels to be produced. Recently, due to increasing demands for LCD panels of larger sizes, there has been a conspicuous trend toward employing mother substrate plates of larger sizes. Similarly, in the fabrication process of large mother plates, the respective plates are repeatedly washed and dried, utilizing the air knife effects in each drying stage. Therefore, it has become necessary for an air knife nozzle to be able to dry substrate plates of large sizes completely and in a reliable manner. On the other hand, in view of the effects on the productivity of LCD panel processing lines, namely, in view of conspicuous degradations in substrate processing efficiency as a whole, it is undesirable to slow down the substrate transfer speed through a drying stage. For these reasons, there has been a great demand for development of an apparatus which can dry substrate plates of large sizes in a secure and reliable manner while being transferred at high speed from one stage to another of a processing line.
With the foregoing situations in view, it is an object of the present invention to provide high precision drying method and apparatus which can dry substrate plates by means of air knife effects quickly in an efficient manner and entirely including rear corner portions of the respective substrate plates.
It is another object of the present invention to provide drying method and apparatus which can dry substrate plate surfaces by air knife effects, free of stains as caused by a spatter of a residual liquid.
It is still another object of the present invention to provide drying method and apparatus which can dry substrate plates, particularly, substrate plates of large sizes quickly in a reliable manner while the substrate plates are being transferred at high speed from one stage to another of a processing line.
According to the present invention, for achieving the above-stated objectives, there is provided an apparatus for drying a substrate plate which is being transferred substantially horizontally by a conveyer means along a predetermined path of transfer, by the use of an air knife nozzle having a slit-like nozzle mouth located at a uniform distance from a drying surface of the substrate plate to spurt a jet of compressed air across width of the substrate plates at a predetermined angle of incidence with respect to a drying surface of the substrate plate from a direction opposite to a transfer direction of the substrate plate to scrape off liquid droplets and films therefrom, characterized in that the apparatus comprises: an incident air angle control means associated with the air knife nozzle to adjust the angle of incidence of jet air with respect to the drying surface of the substrate plate, the incident air angle control means being adapted to make the angle of incidence shallower as soon as the substrate plate reaches a point of entry into an air blasting zone of the air knife nozzle and to make the angle of incidence deeper at latest immediately before the substrate plate reaches a point of disengagement from the air blasting zone.
In this instance, it is desirable for the air knife nozzle to be located obliquely in a plane parallel with a substrate transfer surface of the conveyer means. The incident air angle control means can be constituted either by a descending air angle control means which is adapted to turn the air knife nozzle to vary a descending angle of jet air spurted from the air knife nozzle, or by a current rectifying plate which is located at one side of the path of transfer of the conveyer means in such a way as to make the angle of incidence shallower when the substrate plate comes to a point of entry to the air blasting zone of the air knife nozzle. If desired, these two different types of incident air angle control means can be employed in combination.
In a specific form of the present invention, the descending air angle control means comprises a pair of rotational shafts which are attached to the air knife nozzle in parallel relation with the nozzle mouth to rotatably support the air knife nozzle on a bracket, and a rotational drive means like a pulse motor which is coupled with one of the rotational shafts. Preferably, the descending air control means is adapted to adjust the air descending angle to an angle smaller than 45 degrees at a point of entry of the substrate plate into the air blasting zone of the air knife nozzle, and to an angle larger than 45 degrees at the time of disengagement of the substrate plate from the air blasting zone.
On the other hand, in the case of the current rectifying plate, it is located in the air blasting zone of the air knife nozzle and at one side of the path of transfer of the conveyer means, in parallel relation with side edges of the substrate plate on the side of a leading corner portion thereof to be firstly plunged into the air blasting zone.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawings which show by way of example preferred embodiments of the invention. In this regard, it is to be understood that the preferred embodiments are shown for illustration purposes only and not for limiting purposes.